A wide variety of peroxy compounds is known from the literature as initiators for polymer production. A fairly great number of these are commercially used. See, for example, the product catalogue of Akzo Nobel entitled "Initiators for polymer production", 1992, in which several dozens of initiators for radical polymerization have been mentioned under the trademarks Laurox.RTM., Lucidol.RTM., Perkadox.RTM. and Trigonox.RTM.. Other examples of commercially available initiators are included in the Akzo Nobel range of products sold under the trademarks Butanox.RTM. and Cyclonox.RTM., respectively .sup.1). FNT .sup.1) Laurox.RTM., Lucidol.RTM., Perkadox.RTM., Trigonox.RTM., Butanox.RTM. and Cyclonox.RTM. are registered trademarks of Akzo Nobel N.V.
Commercially available initiators for polymer production may be classified in different chemical groups, which include diacylperoxides, peroxydicarbonates, dialkylperoxides, peroxyesters, peroxyketals, hydroperoxides, and ketone peroxides.
Various ketone peroxides have also been described in the literature as radical polymerization initiators in the (co)polymerization of ethylenically unsaturated monomers.
For example, U.S. Pat. No. 3,149,126 discloses some peroxides derived from the interaction of 1,3- and 1,4-diketones, which are said to be useful inter alia as catalysts in polymerization reactions and in the cross-linking of polymers. The cyclic ketone peroxide identified as Compound VII is only obtained in an analytical amount and described as very volatile, sensitive to shock and exploding with considerable brisance.
U.S. Pat. 3,003,000 discloses a group of peroxides which are said to be useful as catalysts in polymerization reactions and as accelerators of diesel fuel combustion. These formulations may include cyclic ketone peroxides which are formed in side reactions leading to cyclic condensations products. However, the compositions disclosed in this reference clearly contain only minor amounts of cyclic ketone peroxides.
U.S. Pat. No. 3,632,606 discloses fluorinated organic cyclic peroxides which are stated to be much more stable thermally than the corresponding hydrocarbon cyclic peroxides, which can be used, besides their utility as oxidants, as polymerization initiators.
German Offenlegungsschrift 21 32 315 discloses trimeric cycloketone peroxides and in particular tricycloalkylidenperoxides are said to be useful as initiators for polymerization. The disclosure merely concentrates on synthetical aspects of preparing these structures.
British Patent 827,511 discloses formulations of ketone peroxides in paraffinic diesel oil. These formulations may include cyclic ketone peroxides though the goal of this publication is to minimize the amount of cyclic peroxide present in the compositions and thus such compositions contain only minor amounts of cyclic ketone peroxides. Moreover, the reference does not suggest the use of these formulations in polymer production.
British Patent 912,061 discloses formulations of ketone peroxides in dimethyl phthalate and paraffinic diesel oil. These formulations may contain minor amounts of cyclic ketone peroxides. No teaching was given with respect to the possible use as initiators for polymerization.
British Patent 1,072,728 discloses stabilized ketone peroxide compositions formulated in safety solvents which are selected from alcohols and glycols. Such compositions optionally contain diluents other than the safety solvents, such diluents being phthalate esters. These ketone peroxide formulations also contain only minor proportions of cyclic ketone peroxides. Again, no teaching was given as to the possible use as polymerization initiators.
International Patent Applications PCT/EP95/02829 and PCT/EP95/ 02830, both filed on Jul. 14, 1995 and not prepublished, disclose transportable, storage stable cyclic ketone peroxide compositions comprising 1.0-90% by weight of one or more cyclic ketone peroxides and 10-99% by weight of one or more diluents selected from the group of liquid phlegmatizers, plasticizers, solid polymeric carriers, inorganic supports, organic peroxides, and mixtures thereof, as well as the use of these cyclic ketone peroxide formulations in the modification of (co)polymers.
Commercial formulations of methylethyl ketone peroxide and methylisobutyl ketone peroxide are known to be mixtures of several different ketone peroxide compounds, among which the non-cyclic ketone peroxides predominate. However, these ketone peroxides do contain some small quantities of cyclic ketone peroxides which result from side reactions during the preparation of the methylethyl and methylisobutyl ketone peroxides. For example, in commercially available methylethyl ketone peroxides about 1-4% of the total active oxygen content is attributable to cyclic ketone peroxides.
Although the aforementioned peroxides are known for use in the initiation of polymerization reactions, their performance in, for example, acrylic (co)polymerization and the curing of unsaturated polyesters at higher temperatures (i.e. above about 100.degree. C.), is disappointing and they often cause yellowing of the polymer. Furthermore, many commercially available peroxides generate undesired by-products.
Accordingly, there remains a need in the art for polymerization initiators which provide improved performance. These and other objects of the present invention will be apparent from the summary and detailed description of the present invention which follow.